The present invention relates to apparatus for sputter coating of substrates; more particularly, to such apparatus wherein the sputtering target is cylindrical; and most particularly to such apparatus wherein cylindrical targets may be inserted into, operationally retained in, and removed from the surrounding cylindrical cathodes without disassembly of the cathodes.
Cylindrical magnetron sputtering is a useful method for coating three-dimensional complex shapes, such as those used for cutting and forming tools, biomedical devices, optical fibers and so on. Cylindrical magnetron sputtering devices have been described in a series of patents, including U.S. Pat. Nos. 3,884,793; 3,995,187; 4,030,986; 4,031,424; 4,041,353; 4,111,782; 4,116,793; 4,116,794; 4,132,612; 4,132,613; 5,178,743; 5,228,963; 5,437,778; and 5,529,674; all of which are incorporated herein by reference.
Prior art cylindrical magnetrons use a variety of means to create traps for the secondary electrons produced by ion bombardment that are responsible for maintaining the sputtering plasma. Some plasma traps are formed by axial magnetic fields working together with electrostatic wings on the cathode and/or target. Alternatively, the magnetic field and each individual electrode may define other kinds of traps. A variety of examples of such traps are described in the reference patents.
One important advantage of cylindrical magnetrons is that they can use targets that are simple cylinders that slide into a cylindrical cathode body. Therefore, no clamping or bolting is needed to assure that good thermal contact is made between the target and cathode body. As the target temperature rises, the target increases in diameter and clamps more tightly to the water-cooled cathode jacket that surrounds it. In this way a self-limiting temperature is reached as long as an adequate flow of cooling water is maintained. In prior art cylindrical magnetrons, the target is located with respect to the cathode body and held in place by clamps in the ends of the cathode or by flange(s).
It is sometimes advantageous to operate multiple individual cylindrical magnetron cathodes in a single chamber. For example, it may be desirable to have targets of different materials that can be sputtered independently using separate power supplies. Or, in some cases, it is useful to operate two electrically isolated targets with an alternating current power supply in the mid-frequency or radio frequency range. See, for example, the 43rd Annual Technical Conference Proceedings of the Society of Vacuum Coaters, xe2x80x9cAC Reactive Sputtering with Inverted Cylindrical Magnetrons,xe2x80x9d pp. 81-85.
In prior art cylindrical magnetron assemblies having two or more electrically independent cathodes and targets, flanges and clamps typically are used to locate and hold the targets axially within the cathodes. Prior art configurations require that when multiple targets are used that they be installed and removed from both ends of the cathode body. This is very inconvenient, particularly if one end of a cathode body is sealed directly to the vacuum system, as is sometimes the case.
It is a primary object of the invention to provide cylindrical targets that mate with corresponding cylindrical magnetron cathodes, wherein multiple targets may be easily installed from one end of a cathode assembly.
It is a further object of the invention to allow easy removal and installation of targets within a single cylindrical magnetron cathode without the need to remove any fasteners.
It is a still further object of the invention to provide mating cylindrical magnetron targets and cathodes that minimize the area of surfaces subject to the unwanted buildup of sputtered material during the coating process.
Briefly described, a cylindrical magnetron has a cylindrical cathode surrounding a cylindrical target. The cathode is unfeatured at each end, as by a target-supportive flange, such that the target may be removed from or installed into the cathode from either end. The target is positioned and axially retained within the cathode by resilient means operative between the outer surface of the target and the inner surface of the cathode. The invention is especially useful in magnetron assemblies having a plurality of abutting, coaxially disposed magnetrons, wherein all the targets may be removed and replaced from the cathode assembly without requiring disassembly and reassembly of the cathodes.